Abstract: An unthreaded, slip-on fitting for connecting a length of structural pipe to another length of structural pipe and/or to a stationary structural member such as a floor or wall, which is usable in building scaffolding, shelving, railing and the like. The body of the fitting has extending from it a pair of spaced parallel arms between which a locking element is pivotally mounted on a transverse pin spanning the arms. A set screw which is accessible from the exterior of the fitting body when the arms are inserted into the interior of a pipe to which the fitting is connected, engages a portion of the pivotal locking element extending into a cavity in the fitting body communicating with the slot. When the set screw is advanced inwardly, the locking element is pivoted, moving outwardly in opposite directions a pair of pipe clamping projections on the locking element, to grip the interior of the pipe, thereby securing it to the fitting.